what’s with the Gollancz books and yellow covers?

I have two books, The Forever War and I am Legend. both of them have a similar design and overall aesthetic to their covers: bright yellow, a centre photo and names at the top of the cover

they’re both published by Gollancz, but when I look into them I can’t find a reason for this theme in their book covers

why is it they do that? are the books part of a series like Penguin Classics?